1. Field of the Invention
This invention relates to a steering apparatus for an outboard motor, and particularly, to a steering apparatus comprising a helm unit configured to be operated by means of a steering wheel.
2. Description of the Related Art
Conventionally, there has been known a steering apparatus for an outboard motor in which a hydraulic pump is provided on, for example, a helm (steering wheel), and a hydraulic actuator configured to be driven by the hydraulic pump is disposed near the outboard motor. In this steering apparatus, an oil pressure produced by the hydraulic pump serves to redirect the outboard motor. Also known is a mechanical steering apparatus that redirects an outboard motor by transmitting a rotary motion of a steering wheel to the outboard motor by means of a push-pull cable. Since these steering apparatuses are operated manually (or by an operator's power), they require a considerably large operating force, depending on the boat operating conditions, and hence, leave room for improvement.
Thus, as disclosed in, for example, U.S. Pat. No. 7,137,347 B2 (Patent Document 1), a steering apparatus may be contrived such that a sensor for detecting the manipulated variable of a steering wheel is disposed in a helm unit. An electric actuator unit for use as a drive source for steering is driven by electrical signals output from the sensor. In the steering apparatus of this type, the actuator unit is driven based on the sensor output, so that the steering wheel can be turned with little force. In some cases, however, it is undesirable to allow the steering wheel to be turned excessively with little force, so that the helm unit is provided with a friction generating mechanism.
The friction generating mechanism of the steering apparatus described in Patent Document 1 produces a frictional force by means of an electromagnetic actuator. If a power failure occurs in the electromagnetic actuator due to power supply trouble or the like, therefore, the steering wheel may be suddenly turned with little force. In this case, the operation of the steering wheel is perplexing, and in addition, wrong operation of a boat may occur.